Capacitors are commonly used for noise suppression, either in signal lines or in power lines. In power lines, noise suppression can be accomplished by mounting many capacitors along the power line to reduce the impedance level. Such capacitor mounting can increase the size and cost of the system, because the cost of mounting the capacitors can be higher than the cost of the capacitors.
Capacitors can be provided on semiconductor chips having active circuit elements, i.e., “active chips” or can be provided on passive chips containing passive circuit elements such as capacitors, inductors, resistors, etc., for mounting to active chips.
Conventional capacitors in silicon can be of two general types. A first type is used to store charge for each bit in a DRAM chip. A second type is capacitors on passive chips, where the primary focus has been on planar capacitors with very thin dielectric materials having a very high dielectric constant, in a single or multi-layer format. Both types of conventional capacitors can have limitations when applied to decoupling capacitor applications. The first type of capacitor may not be well suited for high capacitance applications, because that type is typically meant for usage at bit level and therefore is purposely designed to have a very small size. The first type typically lacks features needed to store or supply sufficient current as a decoupling capacitor. The second type of capacitor may have a low capacitance density and a low quality factor (efficiency).
Despite all of the above-described advances in the art, still further improvements in capacitors and methods of making capacitors would be desirable.